The End Cap Bearing is used with the 5mm hex shaft recommended for the DUO Build System 15mm Extrusion to provide a low friction rotating shaft support. This bearing is intended to seat in any of the plastic REV DUO brackets with the 9mm ID bearing seat including: REV-41-1313, REV-41-1303 and REV-41-1304. The bearing has a larger diameter flange that helps retain the shaft and bearing against the bracket.